1. Field of the Invention
This invention relates in general to a control system for coating pellets or tablets with a material which forms a film to protect, add an ingredient or improve the appearance of the pellet or tablet.
2. Description of the Prior Art
Machines are known wherein tablets or pellets are coated with a material to apply a film so as to protect, add an ingredient or improve the appearance of the material wherein the tablets are placed in a rotary drum through which processed air is passed while simultaneously spraying the tablets with a solution comprising solids in a carrier. The processing air is cooled, heated, filtered and/or dehumidified and otherwise conditioned so that it removes the carrier from the solution by evaporation so that only the solid materials remain on the surface of each individual tablet and the tablets are dried so they do not stick together.
Such coating processes of the prior art have been operated by trial and error wherein the equipment is operated such that assumptions are made that constant coating conditions exist and changes in the coating and environment are ignored. For example, the process air is assumed to have the same air flow velocity and dew point at all times and in some installations controls are added to condition the process air and hold it constant. However, none of such prior art controls provide constant coating conditions. In many prior art systems, the process air is heated and controlled on the inlet side of the coating machine but the effects on the coating process when the spray solution is turned on are not reflected in the control of the heated air and, therefore, the coating process is being performed in a state of cooling throughout much of the process.
It has been customary in the past, for an operator to try to adjust on a trial and error basis the various parameters of the system but he generally does not have sufficient information to operate a process in an optimum manner.